The present invention relates to a reciprocating valve for double piston concrete pumps. The purpose of such valves is to control the operation of the pump to convey a concrete mix from a supply container into a conveying conduit. The two pump cylinders are arranged in parallel to each other and the housing of the valve control mechanism extends substantially at a right angle to the longitudinal extension of the two pump cylinders. The housing of the valve interconnects the two pump cylinders. Suction ports are connected to the supply container and to the pump and discharge ports are connected to the conveying conduit which, for example, may have a Y-configuration at its valve connected end.
My U.S. Pat. No. 3,889,713 granted on June 17, 1975 describes a reciprocating valve of the above type which has a cylindrical valve housing in which the piston plug operates with the function of "suction-pressure-suction" in that order.
The valve of my above U.S. Patent has several advantages. One advantage is seen in the very short displacement of the valve plug piston. Another advantage is seen in the fact that the suction cross sectional areas from the supply container extend directly through the valve plug piston, whereby sharp bends can be avoided and the concrete mix can flow through passageways having gentle bends of about 75.degree..
However, my above Patent leaves room for improvement, especially with regard to the sealing between the ports in the housing and the respective passageways through the valve plug piston. Since the valve piston is cylindrical, the exit openings or ports around the passageways through the valve plug piston have a configuration which is determined by the cylindrical shape of the piston. Thus, these openings are substantially oval and it is difficult to properly maintain a sealing around these oval openings. The present invention aims at improving the sealing characteristics.
Swiss Pat. No. 372,927 describes a concrete pump having a control piston with a square cross section. The piston is provided with a straight passageway for the concrete during the conveying stroke and with a 90.degree. passageway in the form of an elbow or knee bend connected to the supply container through which the concrete flows during the suction stroke of the pump. This known valve mechanism is suitable for cooperation with a single cylinder pump. It has the advantage of using sealing means in a plane surface rather than in a surface which is bent in accordance with the shape of a cylinder. However, it is a disadvantage that the knee bend requires a 90.degree. deflection of the concrete, which causes a high suction resistance, whereby differential speeds of the concrete flow cannot be avoided. This has several disadvantages. On the one hand the knee bend passageway is subject to substantial wear and tear and on the other hand the consistency of the concrete mix may vary, because the differential speeds tend to demix the concrete mixture.